Metal-clad aluminum alloys



United States Patent METAL-GLAD ALUMINUM ALLOYS Frederick AlfredChampion, Beaconsfield, England, as signor to The British AluminiumCompany Limited, London, England, a company of Great Britain No Drawing.Application August 7, 1951, Serial No. 240,789

Claims priority, application Great Britain October 31, 1950 1 Claim.(Cl. 29--197.5)

This invention relates to composite metals which are composed of two ormore tenaciously adhering layers each containing aluminium as the majorconstituent, the metal of each layer being referred to herein as analuminium-base metal. One of these layers referred to herein as thecore, may be formed from an alloy chosen to provide certaincharacteristics, such as high mechanical strength, While the other orothers, which cover the core on one or both sides and are termed hereincladding, are of substantially pure aluminium or of an alloy selectedfor its high resistance to corrosion and the fact that it is moreelectro-negative than the alloy of the core, so that the cladding willprovide sacrificial protection to the core if the latter becomes locallyexposed by damage to the cladding.

For example, aluminium alloys of high strength but relatively lowcorrosion resistance have been used for the core and covered withcladding of higher corrosion resistance such as aluminium of 99.7%purity. It is also known to apply cladding to a core composed of analuminium-1%% manganese alloy which itself has a good corrosionresistance, the cladding being composed of an aluminium alloy containingzinc or one or more of those metals which when alloyed with aluminiumwill yield a product having the required sacrificial protective action.The metal-clad alloy has a greater resistance to pitting or localcorrosion than either the core or the cladding when exposed separatelyto the corrosive influence.

The metal-clad aluminium alloys so far known to us sulfer from thedefect that they are liable to become discoloured or stained when theycome into contact with certain natural waters although they may beresistant to serious corrosion.

Now it is well-known that aluminium of very high purity, which will bereferred to herein as super purity aluminium and is defined ascontaining at least 99.95% of aluminium, is particularly resistant tocorrosion and discoloration. It is also known that substantially purealuminium of lower purity than super-purity aluminium and aluminiumalloys containing manganese, magnesium, or both, are themselvesrelatively resistant to corrosion, examples of such alloys being thosecontaining l%% manganese, 2 A% magnesium+ /z% manganese, or 1%manganese+I% magnesium. However, if super purity 2,726,436 latented Dec.13, 1955 aluminium is used as a cladding on a core of substantially purealuminium or of such an aluminium alloy having an intrinsically highcorrosion resistance there is not a sufiicient difference in solutionpotential between the core and cladding to ensure the necessarysacrificial protection, and in the event of damage to the cladding,pitting will not be prevented.

We have now found that the necessary difference in solution potentialbetween a cladding of super purity aluminium and a core of highlycorrosion resistant aluminium-base metal of the kind mentioned above,may be ensured by making a controlled addition of copper to the coremetal without materially reducing the natural corrosion resistance ofthe core. In this way it is possible to produce composite aluminium-basemetals which are suitable for the manufacture of articles required towithstand corrosion and to maintain a bright and pleasing appearance,such as trays for domestic use, cooking utensils and kettles.

Accordingly, the present invention consists in a compositealuminium-base metal composed of a core of corrosion resisting aluminiumor aluminium alloy, e. g. an alloy containing 1%% manganese, 2%magnesium+ /z% manganese, or 1% manganese+I% magnesium, and a claddingof super purity aluminium, wherein the core metal contains from 0.10 to0.30%

copper.

The cladding may be on one or both sides of the core. When the core iscomposed of aluminium-1%% manganese alloy the copper content of thelatter is preferably between 0.10 and 0.20%. When magnesium is presentin the core metal slightly more copper may be advantageous.

A composite material in accordance with this invention is particularlysuitable where high resistance to staining and corrosion is required andwhere high mechanical strength is not necessary but the strength ofsuper purity aluminium alone would be inadequate, for example, in themanufacture of hollow-Ware.

I claim:

A composite aluminium-base metal composed of a core of an aluminiumalloy consisting of aluminium plus 1%% manganese and from 0.10 to 0.20%copper and a cladding on at least one face composed of aluminium of atleast 99.95% purity.

References Cited in the file of this patent UNITED STATES PATENTS1,865,089 Dix June 28, 1932 1,873,470 Peek Aug. 23, 1932 1,997,165 BrownApr. 9, 1935 1,997,166 Brown Apr. 9, 1935 2,084,327 Edwards June 22,1937 2,100,411 Reuleaux Nov. 30, 1937 2,240,732 Wood May 6, 19412,312,039 Hoglund Feb. 23, 1943 2,376,681 Gauthier May 22, 19452,586,647 Gresham Feb. 19, 1952

